The broad goals of this proposal are to increase understanding of how surface properties are represented by the visual system. In particular, the project seeks to deepen our understanding of perceptual constancies, the means by which objects and surfaces maintain their appearance in changing contexts. This kind of research falls under the NEI's stated mission of understanding visual function. The first aim of the proposal is to study the visual cues that are important in understanding how scenes affect the perception of surface lightness. In particular, the aim will use psychophysical methods to study the image features that the visual system uses to discount the effects of shadows, illumination changes, and transparency in recovering surface lightness. The second aim will build on the findings of the first;it will seek to identify regions in human visual cortex that respond as the interpretation of shadows and transparencies vary, influencing perceived surface lightness. The third aim will examine the effects of scene interpretation on the representation of the size of surfaces and objects. In this aim, we will study how perceived depth influences the perceived size of objects, and how size constancy mechanisms are represented in visual cortex. PUBLIC HEALTH RELEVANCE Basic mechanisms of visual processing are impaired in a wide range of disabilities including psychiatric conditions such as schizophrenia and autism. One impairment found in a number of conditions is an abnormal effect of context on visual processing. Understanding how the normal visual system processes information and takes into account contextual information may guide development of tests for early diagnosis of such conditions.